The particular problem originally solved by the invention is forming a focusing line along which energy density is uniform, from a monomode or mixed mode laser beam. Obviously, the invention is not restricted to this field, but this problem is interesting to understand the features of the invention.
In many technical fields, focusing laser beam energy along a line or distributing such energy over an extended area, with a uniform energy density, is desired, but known systems either integrate energy during time, preventing real time treatment and generating different treatment conditions, or chop the greatest part of available power, the energy yield being only about 30%.
The present invention relates to an optical system which gives such an energy distribution. The problem presented by such an optical system is that at least a reflecting or refracting surface must have a shape far different from a revolution shape, which shape cannot be obtained by classical processes used in the optical art because surface polishing can be provided only for plane or revolution surfaces.
Some optical systems having a surface which is not strictly a plane or spherical have been provided. For example, French Pat. No. 2 472 198 discloses a process in which a glass blank is cast and one of its faces is polished either as a plane surface or as a spherical surface. Distorting forces are thereafter applied to the blank, for example by vacuum, and the blank which is suitably maintained along its edges is globally distorted. The obtained deformation is very small and corresponds at maximum to some wavelengths of visible light. This deformation is for correcting aberrations of images formed by optical systems.
NASA has also developed a flexible mirror for correcting aberrations in images of planets and satellites observed by space probes. This mirror includes many piezoelectric actuators providing for local distortions of the reflecting surface, the distortions having an amplitude of about a wavelength of visible light.
So, these optical systems use processes providing for very slight changes of the reflecting surface configuration and which do not give its main curvature to the surface.
Distorting mirrors used for example in fairs and attractions are also known. They are constructed from metallic plates distorted in alternate directions to provide enlarged or reduced images. Mirror thickness is constant and obtained shapes are not precisely determined, the distortions being very great. Optical quality of these mirrors is low.